i am a bangladeshi citizen & also green card holder of usa how can i apply for hong kong visit visa

You may either post your visa application to the immigration office of Hk directly or apply for the visa through the China Embassy in Bangladesh. Teh required documents are:
1. Completed application formsID 1003A affixed with a recent-taken passport photo;
2. Photocopy of your travel documents such as personal particulars, date of issue, date of expiry and/or details of any re-entry visa held;
3. Photocopy of your bank statements, savings accounts passbooks or tax receipts to prove that you have adequate funds to cover the duration of your stay in Hk without working;
4. Photocopy of your round-way air tickets;
5. Photocopy of proof of the proposed visit to Hong Kong.